Particles have long been treated for various purposes in streams conveyed over louver decks through which gas is blown upwardly to levitate and treat the particles while the decks are vibrated to advance the particles.
In the case of particle dryers, satisfactory addition or removal of moisture and heat from particles of various materials is governed by a number of factors, such as absorption or release characteristics of the material, relative differences in temperature between the gas and the material, relative mass flows of gas and material, their specific heats and specific volumes, and other constraints, such as temperature limits. These values are approximately the same for any drying device.
Use of vibrating action in conjunction with gas blowing is a well-known technology for particle drying, and several types have been employed commercially. One type uses a vibrating pan to convey the material, while a series of vertical tubes extend down into the material and the drying gases blown through the open bottoms of the tubes and thence into the layer of material. Others direct the drying gas upwards through perforations across the area of a vibrating plate. It is also known to counterbalance the vibrations by using four horizontal decks and phasing their respective vibrations suitably for that purpose. Such counterbalancing requires that all four decks be parallel to each other, and also horizontal if the flow is to be in successive opposite directions as the particles pass from one deck to the next.
When perforated plates are used the openings are exposed and contact the particles with each oscillation of the perforated plate. Particles smaller than the openings fall through the openings into the plenum. Particles of a size near that of the openings become wedged in the openings, which retards the flow of drying gas. These wedged particles also act to retard the flow of material over the perforated plate. There is also a tendency for particles of varying sizes to seek different levels in the mass of airborne particles, so that the particles get varying exposures to the drying air or other gas treatment.
The use of louvers as an alternative to perforations has been known for particle treating purposes. In that case, protective downwardly extending flanges are desirable for purposes of gas flow control and also to oppose entry of particles into the louver openings. However, the downward extent of the flanges would require a compensating upward slope of the main area of the panels if the deck is to be horizontal. This has evidently been considered impractical without returning to perforation of the panels (as shown in Ostberg U.S. Pat. No. 3,089,688 issued May 14, 1963), or else accepting a downward slope of the the deck as a whole (as shown in Cooley U.S. Pat. No. 750,262 issued Jan. 26, 1904).